Field of the Invention
This invention relates to switching of power sources, and in particular, it relates to a switching selector for selecting a power source.
Description of Related Art
Automatic Transfer Switch (ATS) is a circuit that automatically couples one of two alternating current (AC) power sources to a load circuit. ATS can be used to couple an emergency power generator in a system that is normally supplied by a power grid, so that when the power grid is interrupted, the load can be switched to the emergency generator. The ATS must completely isolate the two input power sources.
Power ATS's are typically used in environments where a second power source is provided, such as electrical equipment or electrical appliances that are supplied by a power generator, a computer server room that requires a large power supply, etc. Normally the power is supplied by a main power supply such as the public power grid; but when the main power supply is unstable or down, the power ATS makes a determination and switches to another available stable power source, such as a power generator or an uninterruptible power supply, to continuously supply power to the electrical equipment or appliances. When the main power source is restored, the ATS makes a determination and switches back to the main power source.
However, in a conventional main power detection circuit and switching control circuit, the selecting switch for selecting the power source uses two relays to select and switch to one of the two power sources to supply the load. A drawback of such a structure is that, when one of the relays is malfunctioning or not functioning, the power source selection cannot be made properly.
A second conventional main power detection circuit and switching control circuit requires acquiring the voltage for a second time to make a second determination to confirm that the output power is provided by the selected power source. The second-time acquisition and determination step delays the output of the correct power source.